12 With docile hearts, then, let all Christians hearken to the voice of their Common Father, who would have them, each and every one, intimately united with him as they approach the altar of God, professing the same faith, obedient to the same law, sharing in the same Sacrifice with a single intention and one sole desire. This is a duty imposed, of course, by the honor due to God. But the needs of our day and age demand it as well. After a long and cruel war which has rent whole peoples asunder with it rivalry and slaughter, men of good will are spending themselves in the effort to find the best possible way to restore peace to the world. It is, notwithstanding, Our belief that no plan or initiative can offer better prospect of success than that fervent religious spirit and zeal by which Christians must be formed and guided; in this way their common and whole-hearted acceptance of the same truth, along with their united obedience and loyalty to their appointed pastors, while rendering to God the worship due to Him, makes of them one brotherhood: "for we, being many, are one body: all that partake of one bread."
Source: Mediator Dei (Vatican.va)